BF: fix Cython TypeError from negative indices to tuples

It looks as though Cython now raises a TypeError if you use negative indices
with the boundscheck decorator, even if these indices are to tuples.

Use positive indices instead.
Merge pull request #180 from matthew-brett/cython-indexing-fix

BF: fix Cython TypeError from negative indices to tuples
RF - fix disperse_charges so that a large constant does not cause the potential to blow up.
DOC: replace soureforge.net links with nipy.org

Change canonical nipy web address.
Merge pull request #185 from matthew-brett/no-sourceforge-links

DOC: replace soureforge.net links with nipy.org
Merge pull request #183 from ecaruyer/fix-for-issue-181

OPT: Modified dipy.core.sphere_stats.random_uniform_on_sphere, cf issue #181
Merge pull request #182 from MrBago/disp-charges-constant

RF - fix disperse_charges so that a large constant does not cause the po...
Merge remote branch 'nipy/master' into HEAD
RF - add subdivide test to compare.py
Merge pull request #1 from MrBago/profile_dispcharges

Profile dispcharges